The thermoelastic behaviour of semicrystalline and of glassy poly(ether-ether-ketone)

A thermoelastic evaluation, based on simultaneous measurements of the mechanical work and of the concomitant heat of deformation by a stretching micro calorimeter, was performed on semicrystalline and glassy PEEK. The objective of this study was to utilize the sensitive technique to detect differences that would account for observed effects of micro structure on mechanical performance. A clear difference was detected beyond a 0.6% strain, where the behaviour of glassy PEEK began to exhibit inelastic features such as yielding and plastic deformation. This difference between the glassy and the semicrystalline polymers was considered the reason for the superior mechanical fatigue and fracture properties produced by the latter micro structure.     

Comment on ‘Thermoelsatic analysis of the functionally graded rotating disk’

In their paper, Hosseini Kordkheili and Naghdabadi (2007) [1] have obtained the Navier thermoelastic equation, along with some coefficients, incorrectly. This has resulted in considerable error in their numerical results. Other authors in this field frequently use the work of Kordkheili and Naghdabadi in their own calculations. Asghari and Ghafoori (2010) [2] is an example of another work that has used the wrong Navier thermoelastic equation directly in their work. It is clear there is a need for corrected formulations, which will be presented here.     

Porothermoelastic Analysis of the Response of a Stationary Crack Using the Displacement Discontinuity Method

Thermally induced volumetric changes in rock result in pore pressure variations, and lead to a coupling between the thermal and poromechanical processes. This paper examines the response of a fracture in porothermoelastic rock when subjected to stress, pore pressure, and temperature perturbations. The contribution of each mechanism to the temporal variation of fracture opening is studied to elucidate its effect. This is achieved by development and use of a transient displacement discontinuity (DD) boundary element method for porothermoelasticity. While the full range of the crack opening due to the applied loads is investigated with the porothermoelastic DD, the asymptotic crack opening is ascertained analytically. Good agreement is observed between the numerical and analytical calculations. The results of the study show that, as expected, an applied stress causes the fracture to open while a pore pressure loading reduces the fracture width (aperture). In contrast to the pore pressure effect, cooling of the crack surfaces increases the fracture aperture. It is found that the impact of cooling can be more significant when compared to that of hydraulic loading (i.e., an applied stress and pore pressure) and can cause significant permeability enhancement, particularly for injection/extraction operations that are carried out over a long period of time in geothermal reservoirs.     

Thermoelastic analysis of a functionally graded rotating disk

A semi-analytical thermoelasticity solution for hollow and solid rotating axisymmetric disks made of functionally graded materials is presented. The radial domain is divided into some virtual sub-domains in which the power-law distribution is used for the thermomechanical properties of the constituent components. Imposing the necessary continuity conditions between adjacent sub-domains, together with the global boundary conditions, a set of linear algebraic equations are obtained. Solution of the linear algebraic equations yields the thermoelastic responses for each sub-domain as exponential functions of the radial coordinate. Some results for the stress, strain and displacement components along the radius are presented due to centrifugal force and thermal loading. Results obtained within this solution are compared with those of a finite element analysis in the literature. Based on the results, it is shown that the property gradation correlates with thermomechanical responses of FG disks.     

Transient thermal stress intensity factors for an internal longitudinal semi-elliptical crack in a thick-walled cylinder

In this paper, the stress intensity factors are derived for an internal semi-elliptical crack in a thick-walled cylinder subjected to transient thermal stresses. First, the problem of transient thermal stresses in a thick-walled cylinder is solved analytically. Thermal and mechanical boundary conditions are assumed to act on the inner and outer surfaces of the cylinder. The quasi-static solution of the thermoelasticity problem is derived analytically using the finite Hankel transform and then, the stress intensity factors are extracted for the deepest point and the surface points of the semi-elliptical crack using the weight function method. The results show to be in accordance with those cited in the literature in the special case of steady-state problem. Using the closed-form relations extracted for the transient thermal stress intensity factors, some conclusive results are drawn.     

Some theorems in the theory of microstretch thermopiezoelectricity

The electromagnetic theory of microstretch thermoelasticity is an adequate tool to describe the behaviour of porous bodies, animal bones and solids with deformable microstructures. In this paper we study the linear theory of microstretch thermopiezoelectricity. First, we establish a reciprocity relation which involves two processes at different instants. This relation forms the basis of a uniqueness result and a reciprocal theorem. Then, we study the continuous dependence of solutions upon initial data and body loads. A variational characterization of solutions is also presented. Finally, we investigate the effect of a concentrated heat supply and the effect of a concentrated volume charge density in an unbounded homogeneous and isotropic body.     

Fractional heat conduction equation for an infinitely generalized,thermoelastic, long solid cylinder

In this work, we consider the one-dimensional problem for an infinitely long solid cylinder in the context of the theory of generalized thermoelasticity with one relaxation time. The heat conduction equation with the Caputo fractional derivative of order α is used. The curved surface of the cylinder is assumed to be in contact with a rigid surface and is subjected to constant heat flux. By means of the Laplace transform and numerical Laplace inversion the problem is solved. Numerical computations for the temperature, displacement and stress distributions are carried out and displayed graphically as well as the results are discussed comprehensively.     

Mean stress dependence of the thermoelastic constant

The SPATE 8000 thermoelastic stress analyser has been used to demonstrate the mean stress dependence of the thermoelastic constant. This dependence has potential application in the measurement of residual stress provided the material has not yielded.     

On Reflection and Transmission of p- and Sv-Waves Phenomena at the Interface Between Solid-Liquid Media with Magnetic Field and Two Thermal Relaxation Times

In this research, we studied the reflection and transmission of thermoelastic wave at a solid-liquid interface under influence of two thermal relaxation times and magnetic field. The governing equations are introduced taking into consideration Green-Lindsay theory and Maxwell's stresses. After solving the governing equations, we found the two reflections and transmission coefficients of incident p-(primary) and SV- (Shear Vertical) waves in the presence of thermal relaxation times and a magnetic field. The boundary conditions at the interface have been applied. The appropriate expressions to find the amplitude ratios for the two incidence waves (p- and SV-waves) have been obtained. A numerical calculation is made for the reflection and transmitted coefficients of the incident waves, in which we study the effect of thermal relaxation times and magnetic field. The results obtained are presented graphically for the effect of magnetic field and relaxation times to display the phenomena physical meaning.     

Thermo-mechanical coupling in cylindrical bending of sandwich plates

This paper presents an exact solution of linear elasticity theory for bending of sandwich plate-like beams due to temperature difference at the plate faces. It is assumed that the heat flow is stationary. The exact solution yields the temperature profile, stress and displacement distribution across the plate thickness. The analytical results are complemented by an example of a simply-supported sandwich beam.